The Veil

When the universe was split into two by Etheria there was a sort of barrier formed between them called the veil. The veil has a sort of intelligence that gives it the ability to repair itself and make decisions that would keep the barrier between Thera and the Aether. In places where the veil is thin it "knots" itself to strengthen the area, creating a Veil Core in Thera. When there is a tear too big for the veil to quickly repair it will "fold" itself to fix the hole causing a reality cascade.